Classification of United States light water reactors by dominant core melt frequency contributors

In the past ten years a relatively small number of Light Water Reactors (LWRs) in the United States (US) have been the object of intense risk analysis. These plants have been used as surrogates to evaluate generic safety issues at other plants. There are many problems with the surrogate approach to generic nuclear safety research, the most obvious being that nuclear plants in the US are almost always different from one another in ways that affect plant risk. To address this problem, the Accident Sequence Evaluation Program (ASEP) is classifying LWRs in the US by dominant core melt sequence contributors - excluding external events. These contributors are identified through examination of approximately 100 US LWRs. Although the ASEP grouping scheme is complex, it should be considered in generic studies to better understand generic safety issues.